In May 2013, the Food and Drug Administration (FDA) approved the first cancer treatment drug containing an alpha-emitting isotope. Pb-212 and Bi-213 are known alpha-emitting isotopes potentially useful for this purpose. See, e.g., Yong, K. et al., “Application of 212Pb for Targeted α-particle Therapy (TAT): Pre-clinical and Mechanistic Understanding through to Clinical Translation,” AIMS Med Sci. 2015; 2(3): 228-245, published online 2015 Aug. 18. doi: 10.3934/medsci.2015.3.228; and Dekempeneer, Y. et al., “Targeted alpha therapy using short-lived alpha-particles and the promise of nanobodies as targeting vehicle,” Expert Opin Biol Ther. 2016 Aug. 2; 16(8): 1035-1047, published online 2016 May 19. doi: 10.1080/14712598.2016.1185412.